1. Field of the Invention
The invention relates to a Schottky diode and, in particular, to a Schottky diode with high antistatic capability.
2. Description of Related Art
Schottky diode is a diode with lower forward voltage drop and allows high-speed switches. A metal-semiconductor junction is used as a Schottky barrier for current rectification, different from the P-N junction of normal diodes that are purely formed between semiconductors. The characteristics of a Schottky barrier lower the forward voltage drop of the Schottky diode, and increase the switching speed.
With reference to FIG. 3, the Schottky diode mainly has an N− type doped drift layer 81 formed on an N+ type doped layer 80. The N− type doped drift layer 81 is formed with an embedded protection ring 82 in which a P-type doped area is formed. The surface of the N− type doped drift layer 81 is further formed with an oxide layer 83 and a metal layer 84. The contact region between the metal layer 84 and the N− type doped drift layer 81 and the P-type doped area forms a Schottky barrier 85. Moreover, the bottom surface of the N+ type doped layer 80 is formed with a metal layer as a bottom electrode 86.
In the above-mentioned structure, free electrons in the N− type doped drift layer 81 have a lower energy level than those in the metal layer 84. Without a bias, the electrons in the N− type doped drift layer 81 cannot move to the metal layer 84. When a forward bias is imposed, the free electrons in the N− type doped drift layer 81 have sufficient energy to move to the metal layer 84, thereby producing an electric current. Since the metal layer 84 does not have minor carriers, electric charges cannot be stored. Therefore, the reverse restoring time is very short. According to the above description, the Schottky diode uses the junction between the metal and the semiconductor as the Schottky barrier for current rectification. It is different from the PN junction formed by semiconductor/semiconductor junction in normal diodes. The characteristics of the Schottky barrier render a lower forward voltage drop for the Schottky diode. The voltage drop of normal PN junction diodes is 0.7-1.7 volts. The voltage drop of the Schottky diode is 0.15-0.45 volts. The characteristics of the Schottky barrier also increase the switching speed.
With reference to FIG. 4, the characteristic curve of the Schottky diode shows the relation between the forward voltage V and the current I and relationship between the reverse breakdown voltage and the current I. The characteristic curve indicates that as the current I becomes larger, the forward voltage V also becomes higher. The rise in the forward voltage definitely affects the characteristics and applications of the Schottky diode. On the other hand, to prevent electronic products from being damaged by electrostatics, whether the Schottky diode has high antistatic capability is an important issue.